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CH302 Vanden Bout/LaBrake Fall 2013
Vanden Bout/LaBrake/Crawford
CH301
WHY IS EVERYTHING SO DIFFERENT? Gas, Liquid or Solid?
UNIT 3 Day 5
CH302 Vanden Bout/LaBrake Spring 2013
Important Information
HW08 DUE Tue 9AM
Laude LM Lecture 16 & 17
Unit3Day5-CrawfordWednesday, October 23, 20132:58 PM
Unit3Day5-Crawford Page 1
CH302 Vanden Bout/LaBrake Fall 2013
What are we going to learn today?
Use VSEPR, VB & MO to get a better picture of POLAR and NONPOLAR MOLECULES
Recognize different molecules have different physical properties
Classify Intermolecular Forces (IMF)
CH302 Vanden Bout/LaBrake Fall 2013
Chemists use a localized electron theory and a delocalized electron theory to help predict and explain bonding in molecules, these models are referred to respectively as:a) VSEPR, VBb) VB, VSEPRc) VB, MOd) MO, VBe) VSEPR, MO
QUIZ: iClicker Question 1
Unit3Day5-Crawford Page 2
CH302 Vanden Bout/LaBrake Fall 2013
COMBINE VB and MO THEORIES
VB for sigma bonds
CH302 Vanden Bout/LaBrake Fall 2013
MO for the pi bond Where are the electrons?
Delocalized around the molecule
COMBINE VB and MO THEORIES
Unit3Day5-Crawford Page 3
CH302 Vanden Bout/LaBrake Fall 2013
Visualize Ethanol
We use VSEPR and VB to get visual image
We predict polarity just from the ball and
stick model
CH302 Vanden Bout/LaBrake Fall 2013
Chemical Composition & Shape
What are the Physical Properties?
Is the molecule a gas or a liquid?
CH302 Vanden Bout/LaBrake Fall 2013
Chemical Composition & Shape
What are the Physical Properties?
What is the density of a liquid?
Unit3Day5-Crawford Page 4
CH302 Vanden Bout/LaBrake Fall 2013
Chemical Composition & Shape
What are the Physical Properties?
What is the density of a liquid?
CH302 Vanden Bout/LaBrake Fall 2013
Physical Properties
What dominates the interaction in
condensed phases?
What are these forces? How are they
classified?
Define Intermolecular Forces (IMF).
NOTE: Remember Tape, Charged Rods and Liquids
Unit3Day5-Crawford Page 5
CH302 Vanden Bout/LaBrake Fall 2013
Open Course Pack to Page 79IMF Unit-Electrostatic Forces-Liquids
1. Draw the Lewis Structures2. Identify any trends.
Activity
Relationship between Chemical Formula and Boiling Point
1.
2.
3.
4.
5.
CH302 Vanden Bout/LaBrake Fall 2013
Identify a Few Trends
CH302 Vanden Bout/LaBrake Fall 2013
Intermolecular Forces
The dominate force in chemistry is Coulombic
Unit3Day5-Crawford Page 6
CH302 Vanden Bout/LaBrake Fall 2013
Intermolecular Forces
The dominate force in chemistry is Coulombic
CH302 Vanden Bout/LaBrake Fall 2013
Intermolecular Forces
The dominate force in chemistry is Coulombic
Qualify the word “intermolecular”
The boiling point of NaCl is 1413 °C. Why is it so high?
Unit3Day5-Crawford Page 7
CH302 Vanden Bout/LaBrake Fall 2013
The molecule is in a condensed phase, but not
ionic
A molecular condensed phase is a molecular
liquid or a molecular solid
“PARTICLE IS A MOLECULE”
Intermolecular Forces
CH302 Vanden Bout/LaBrake Fall 2013
Intermolecular Forces: Dipole-Dipole
Attractive force between partial
negative end of one molecule
and partial positive end of
another molecule.
Strength depends on distance
and dipole moment.
Unit3Day5-Crawford Page 8
CH302 Vanden Bout/LaBrake Fall 2013
ALL NONPOLAR COMPOUNDS ARE
GASES:
A)TRUE
B)FALSE
Poll: iClicker Question 2
CH302 Vanden Bout/LaBrake Fall 2013
ALL NONPOLAR COMPOUNDS ARE NOT GASES
Look at the Data
Methane
BP: -161 C
Nonpolar
Gas
Ethane
BP: -88.7 C
Nonpolar
Gas
Hexane
BP: 68.7 C
Nonpolar
Liquid
Unit3Day5-Crawford Page 9
CH302 Vanden Bout/LaBrake Fall 2013
Intermolecular Forces: Fact Check
How is it possible for Hexane and Carbon Tetrachloride to
exist as liquids?
How is it possible for Octane to have a higher boiling point
than Water?
How is it possible for Water and Ethanol to be attracted to a
charged rod, whereas Hexane and Carbon Tetrachloride
are not attracted to it?
There must be an ELECTROSTATIC ATTRACTION!
CH302 Vanden Bout/LaBrake Fall 2013
Intermolecular Forces: Induced Dipole-
Induced Dipole
Induced Dipole-Induced
Dipole interactions exist in
ALL condensed substances
Caused by induced dipoles,
which come and go in
nonpolar molecules and
atoms
CH302 Vanden Bout/LaBrake Fall 2013
Intermolecular Forces: Induced Dipole-
Induced Dipole
This type of IMF goes by several different names:
Induced dipole – Induced dipole
Dispersion Forces
London Forces
Van der Waal’s Forces
Unit3Day5-Crawford Page 10
CH302 Vanden Bout/LaBrake Fall 2013
Intermolecular Forces: Induced Dipole-
Induced Dipole
This type of IMF goes by several different names:
Induced dipole – Induced dipole
Dispersion Forces
London Forces
Van der Waal’s Forces
CH302 Vanden Bout/LaBrake Fall 2013
Consider the following alkane data.
A molecule with a MW of 80 g mol-1 will be a
_______ at room temperature.
A. Solid B. Liquid C. Gas
Poll: iClicker Question 3
Alkane MW [g mol-1] BP [°C]
Methane 16 -161
Ethane 30 -88.7
Propane 44 -42.1
Butane 58 -0.5
Pentane 72 36.1
Hexane 86 68.7
CH302 Vanden Bout/LaBrake Fall 2013
Now consider an array of atoms and molecules
The IMF strength is dependent on
A. MW B. Shape C. Polarizability D. B&C
Poll: iClicker Question 4
Alkane MW [g mol-1] BP [°C]
Helium 4 -268.9
Krypton 83 -153.2
Propane 44 -42.1
CCl4 154 77
Octane 114 126
Unit3Day5-Crawford Page 11
CH302 Vanden Bout/LaBrake Fall 2013
Now consider an array of atoms and molecules
The IMF strength is dependent on
A. MW B. Shape C. Polarizability D. B&C
Poll: iClicker Question 4
Alkane MW [g mol-1] BP [°C]
Helium 4 -268.9
Krypton 83 -153.2
Propane 44 -42.1
CCl4 154 77
Octane 114 126
CH302 Vanden Bout/LaBrake Fall 2013
Polarizability
Induced Dipole-Induced
Dipole forces exist in ALL
condensed substances
Strength depends on
polarizability
CH302 Vanden Bout/LaBrake Fall 2013
Shape
Why can’t the charged glass rod induce a dipole?
Distance Dependence is HUGE
This is why shape is so important – how close can
the individual atoms get to each other in space?
Common examples are oils vs. fats, and plastic
wrap vs. milk jugs
FAVORITE ANALOGY - VELCRO
Unit3Day5-Crawford Page 12
CH302 Vanden Bout/LaBrake Fall 2013
We can evaluate SIMILAR molecules
Alkane MW [g mol-1] BP [°C]
Methane 16 -161
Ethane 30 -88.7
Propane 44 -42.1
Butane 58 -0.5
Pentane 72 36.1
Hexane 86 68.7
Ionic MW [g mol-1] BP [°C]
LiCl 42 1382
NaCl 58 1413
KCl 74 1420
Alcohol MW [g mol-1] BP [°C]
Methanol 32 65
Ethanol 46 78
Propanol 60 97
CH302 Vanden Bout/LaBrake Fall 2013
Explore Real Data
Activity (IMF Unit-Electrostatic Forces-Liquids)
Course Pack Page 80
CH302 Vanden Bout/LaBrake Fall 2013
Poll: iClicker Question 5
The BP of Sn hydride less than the BP of the Te hydride because:
a) The Sn compound has a larger dipoleb) The Sn compound has a smaller dipolec) The Sn compound is more polarizable d) The Sn compound is less polarizablee) Sn was abducted by aliens, obviously.
Unit3Day5-Crawford Page 13
CH302 Vanden Bout/LaBrake Fall 2013
Poll: iClicker Question 5
The BP of Sn hydride less than the BP of the Te hydride because:
a) The Sn compound has a larger dipoleb) The Sn compound has a smaller dipolec) The Sn compound is more polarizable d) The Sn compound is less polarizablee) Sn was abducted by aliens, obviously.
CH302 Vanden Bout/LaBrake Fall 2013
Poll: iClicker Question 6
The BP of S hydride less than the BP of the Te hydride because:
a) The S compound has a larger dipoleb) The S compound has a smaller dipolec) The S compound is more polarizable d) The S compound is less polarizablee) The S compound has more friends
Unit3Day5-Crawford Page 14
CH302 Vanden Bout/LaBrake Fall 2013
Poll: iClicker Question 7
BP does not seem to follow the trend for which period?
a) 1b) 2c) 3d) 4e) 5
CH302 Vanden Bout/LaBrake Fall 2013
Intermolecular Forces: Dipole-Dipole
A special type of dipole-dipole forces is particularly strong,
called HYDROGEN BONDING
Occurs in compounds with a H bound directly to F, N or O
Strength depends on
distance and dipole moment,
where a big dipole indicates
a closer distance
Unit3Day5-Crawford Page 15
CH302 Vanden Bout/LaBrake Fall 2013
Poll: iClicker Question 8
The BP of O hydride is higher than the BP of the Tehydride because:
a) The O compound has a larger dipoleb) The O compound has a smaller dipolec) The O compound is more polarizable d) The O compound is less polarizablee) The O compound has more hydrogen bonding
CH302 Vanden Bout/LaBrake Fall 2013
Consider the following molecules.
A B C D E
Which molecule has the lowest boiling point?
Poll: iClicker Question 9
Unit3Day5-Crawford Page 16
CH302 Vanden Bout/LaBrake Fall 2013
Consider the following molecules.
A B C D E
Which molecule has the highest boiling point?
Poll: iClicker Question 10
CH302 Vanden Bout/LaBrake Fall 2013
Consider the following molecules.
-24 C 56 C 78.5 C 188.2 C 554 C
The NUMBER of Hydrogen Bonds is
Very Important
0 1 2 30H-Bonds
BP
Unit3Day5-Crawford Page 17
CH302 Vanden Bout/LaBrake Fall 2013
There are also IMF between different “types” of compounds
Can you think of any examples of the following?
Ion – Dipole
Dipole – Induced dipole
Intermolecular Forces
CH302 Vanden Bout/LaBrake Fall 2013
Strength Varies with TYPE
Intermolecular Forces
Unit3Day5-Crawford Page 18
CH302 Vanden Bout/LaBrake Fall 2013
PHYSICAL PROPERTIES DEPEND ON COMPOSITION & SHAPE OF COMPOUND
CLASSIFY INTERMOLECULAR FORCESION-ION vs. DIPOLE-DIPOLE vs. INDUCED DIPOLE –
INDUCED DIPOLE
PREDICT WHAT TYPE OF IMFs EXIST FOR A PARTICULAR COMPOUND
What have we learned today?
CH302 Vanden Bout/LaBrake Fall 2013
Learning Outcomes
Define the three major types of intermolecular forces (IMF) discussed in class: dipole-dipole, H-bonding, and dispersion (London, van der Waals,induced dipole-induced dipole, instantaneous dipole-instantaneous dipole)
Explain how molecular size and shape affect the magnitude of the dispersion forces
Unit3Day5-Crawford Page 19
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